Various types of electronic appliances include many devices such as a microcomputer, a sensor, and a driver. Since, the respective devices may not always have the same power-supply voltage level to be required, it is necessary to generate an optimum power-supply voltage by a linear regulator.
When the output voltage of the linear-regulator varies due to the effect of a power supply noise, each device operates unstably. A power-supply noise rejection ratio (PSRR: Power Supply Rejection Ratio) is an indicator to indicate the degree of effect of power supply noise to the linear regulator output. The PSRR is expressed with a ratio of power-supply voltage variation and output voltage variation, indicating that, when the power-supply voltage variation occurs, as the PSRR ratio becomes higher, the degree of output voltage variation becomes lower. It can be said that a high PSRR value means high tolerance to the power supply noise.
However, if the PSRR value is raised, power consumption may increase.